Actually, looking behind the Beatles you can see written on the wall "Suzie Wong", which (according to my friend Google!) was a play performed at the Prince Of Wales Theatre in London in the late 1950s/early 1960s. The Beatles performed at that same theatre for the Royal Variety Performance in November 1963, so that photo could have been taken then. The "wall" actually looks like it is part of a wooden stage set.Wikipedia doesn't list Sir John Gielgud as one of the performers in that Royal Variety show (http://en.wikipedia.org/wiki/List_of_Royal_Variety_Performances) but as a well-known actor and director he could have been among the audience that night.

The Beatles played the same theatre only once more - in May 1964 as part of Epstein's "Summer Pops" series of concerts - so that is another possibility.